The following discussion of the prior art is provided to place the invention in an appropriate technical context and enable the advantages of it to be more fully understood. It should be appreciated, however, that any discussion of the prior art throughout the specification should not be considered as an express or implied admission that such prior art is widely known or forms part of common general knowledge in the field.
There are various well known and conventional methods for repairing pipes, in particular underground pipes. In recent years, new mechanisms have developed for providing a plastic internal liner for the damaged pipe. This permits the damaged pipe to remain in place during and after repair, limits excavation and provides a rapid and relatively inexpensive repair.
One particular technique, and which is subject of several Australian and overseas patents, involves lining a damaged pipe with a helically wound pipe formed from an extruded plastic web (sometimes referred to as a “profile”) with interlocking male and female edges. The plastic web is commonly formed from PVC, however other plastics materials could alternatively be used. In one such form, the pipe liner is installed as shown in FIG. 1. A winding machine 10 is lowered into the maintenance hole 20 and positioned at its base. A spool 40 of the profile is provided at the surface. The profile is fed to the winding machine 10 where it is helically wound into the liner 60. As the profile is wound, the male and female edges of adjacent profile are interconnected to form the liner 60.
The profile is pulled into the winding machine 10 using a hydraulic drive. The machine 10 has several radial arms with rotating end rollers causing the whole machine to rotate inside the host pipe and lay the profile against the wall of the host pipe. While the machine rotates it also moves along the host pipe making the new pipe liner 60 behind it.
Ideally, the new liner pipe is laid intimately against the wall of the existing host pipe. For example to rehabilitate a pipeline at internal diameter 1000 mm, a liner of external diameter 1000 mm would be desirable, and depending on the wall thickness of the new pipe the internal pipe is therefore reduced by this amount. This allows the pipe to be installed at a maximum diameter to optimise hydraulic efficiency. An example of this technology is that which has been developed and patented by Rib Loc Pty Ltd under (Australian Patent No. 746923).
There are, however, a number of inherent limitations of the technology described in AU 746929, including:
(i) The profile requires a minimum longitudinal stiffness/rigidity such that the male/female locking members are able to engage without the need for external compressive force acting on them. This limits the range of profiles that can be used.
(ii) The apparatus described in AU 746929 relies on the tension in the profile to engage the locking members. Therefore, as the diameter of the wound pipe increases the size of the “entry angle” becomes progressively shallower, where the locking members will no longer engage properly and therefore limits the diameters that the profile can be wound to (see FIG. 2 for the “entry angle”).
(iii) The invention which is the subject of AU 746929 relies on the forces acting on the driven strip and the reactive force provided by tension in adjacent convolution(s) of the profile for the locking members to properly engage. This can mean less reliable engagement. Should the locking members not engage during the installation, the liner would need to be repaired or re-installed.
It is therefore an object of the present invention to overcome or ameliorate at least one of the disadvantages of the prior art or to provide a useful alternative.